1. Field of the Invention
The present invention relates to a voice-data processing circuit for and a voice-data processing method of simultaneously processing two voice data.
2. Description of Related Art
In general, a voice-data processing circuit that can simultaneously process two voice data is provided with two sets of an analog input source switch, an A/D converter, a signal-processing means, a D/A converter, and so on. Therefore, such a voice-data processing circuit can process two sets of analog input signals which are different from each other by making them pass through different signal paths, and then outputs the processed signals as voices independent of each other. In case where an analog signal is input to this type of DSP (Digital Signal Processor), it is applied to a first A/D converter or a second A/D converter and is then converted into voice data. However, when selecting an FM signal as an input source, the DSP has no other choice but to use the second A/D converter in order to convert the FM signal into voice data. When outputting different analog audio sources other than FM signals by way of the different signal processing paths, respectively, if the DSP tries to change the input source applied to one of the two paths via which a voice is output by using the first A/D converter to an FM signal, and to maintain the current input source applied to the other one of the two paths via which a voice is output by using the second A/D converter, the DSP has to switch the currently-selected analog source from the other path via which a voice is output by using the second A/D converter to the path via which a voice is output by using the first A/D converter in order to input the FM signal to the second A/D converter.
However, this results in a switching of an analog switch intended for selection of an input source and located at the front of the first A/D converter, and therefore an unusual sound comes out from the corresponding signal processing path. There has been provided a method of performing a muting process in order to prevent a generation of such an unusual sound (for example, refer to Philips Semiconductors User Manual SAA7709H/N107 Software Audio part Version 1.0, pages 30 to 31 and 193 to 194).
A problem with the prior art voice-data processing circuit disclosed by the above-mentioned non-patent prior art reference is however that a muting process causes a sound skip and there causes a feeling of wrongness in a voice (i.e., a voice output via a signal processing path that is switched from the first A/D converter to the second A/D converter) outputted via a signal processing path on which no switching between input sources is performed.